Does 2Factor charge for failed sms otps?

No, You are not charged for failed OTPs.2Factor is the only bulk sms otp service provider in India, who offers SLA based pricing. Our SLA for critical sms otp and voice OTP services is,

SMS OTP: We charge customers only if,- SMS OTP is delivered ( Pay per delivered OTP )- SMS OTP is delivered within 15 seconds- SMS OTP is delivered without the help of fallback / fail-over logic

If SMS OTP could not be delivered within 15 seconds ( for what so ever reasons ) we not only refund the OTP credit in real-time, but also try to deliver OTP via backup carrier ( SMS Channel ) for free of cost